As the demand for less invasive medical diagnosis and treatment grows, techniques for examining living tissue on a microscopic scale have become increasingly important. Conventional medical endoscopes, with diameters that range from about 1 mm to over 1 cm, provide physicians with a view of the surface of the walls of lumens in the gastrointestinal, pulmonary, and reproductive tracts. However, seeing below the surface of the tissue is essential to detect and characterize lesions associated with cancer and other pathological conditions. Optical Coherence Tomography (OCT), an interferometric imaging technology, is ideally suited to subsurface visualization of biological tissue via small-diameter probes and catheters.
Existing OCT scanning methods have primarily relied on galvanometers to scan the probe beam linearly across the target material. Alternatively, existing systems use a rotary motor to scan the probe beam circumferentially inside a lumen with a circular cross section. Neither method satisfies the need to view targets in front of the probe through a narrow orifice. As a result, a specific need exists for a probe that can visualize blocked coronary arteries, with the goal of characterizing the composition of the plaque and guiding atherectomy devices designed to dissect or remove the blockage. A need also exists for an OCT probe for insertion in a needle that would allow an operator to view tissue structures as the needle advances. A further need exists for probes that can be inserted through working channels of endoscopes designed for forward-directed imaging.
To the extent that forward-directed optical scanning is possible, such implementations are impractical for many applications. This follows because they generate non-linear scan patterns that are difficult to interpret, require complex and expensive mechanisms, or require probes with excessively large diameters. Furthermore, systems that depict actuators and movable mechanisms positioned at or near the distal end of the fiber endoscope conflict with the need to make the distal end as small as possible. What is needed, therefore, is a catheter design that enables forward-directed scanning at a distal location such that the distal portion of the probe can be significantly miniaturized and simplified compared to the known art.